in your /etc/inittab and reboot the box.
Please note, that SL5.0 installation did not recognise my card: ATI X1600 [Asus A6000KT laptop] so I had no X running and the default init mode was 3 [not 5]. YMMV.

I still do not know how to rebuild the kernel module for the different kernels.
By default the kernel module is being build for the current kernel [uname -r]
Today was the first security kernel upgrade revision 2.6.18-8.1.4.el5.
So after new kernel installation I repeated the same procedure and installed new kernel module with